There is a known method for determination of thermal properties of solid materials, which is described in RF patent No. 2212653 and includes the pulse heating of a solid body, measurements of the solid body temperature on the solid body surface, and the processing of the electronic signal of the solid body temperature. The main disadvantage of the known method consists in the fact that complicated processing of measurement data is required in case of the pulse heating, which reduces the measurement accuracy and increases considerably the measurement cost.
The closest analogue of the suggested method is the method for determination of thermal properties of solid materials, which is described in the article “Flat Sonde Method for Determination of Thermal Properties of Rock in Wells and Mines” by P. I. Filippov, in the book “Methods for Determination of Thermal Properties of Rock”, Moscow, Nauka Publishing House, 1970, pages 107-111. The known method includes the heating of the solid body surface by a flat heater restricted by a heat insulator from one side, the registration of the heater temperature during the heating, and the determination of the thermal conductivity and thermal diffusivity of the solid body, based on the heater temperature data. However, this method has serious disadvantages which limit its area of application. These disadvantages include a low accuracy of measurements taken on cylindrical, conical, spherical, elliptical, rough and irregular surfaces, as well as in wells filled with fluid. These disadvantages result from the fact that the heater temperature is registered not on the entire heater surface in contact with the solid body, but only in the small area where a point temperature sensor is located, and that it is impossible to achieve the required thermal contact of the heater and the temperature sensor with the solid body throughout the heater surface and the temperature sensor surface. The measurement process is limited by the heater's operating period only, and it is impossible to take into account the heat loss from the heater into the adjacent heat insulator, which is necessary for the registration of the changes in the contact thermal resistance between the heater and the solid body surface. A serious disadvantage consists in the fact that the measurement data may be considerably distorted due to the effect of the thermal convection (which is inevitable in case of a heat source present in the well fluid), and that the equation used as an algorithm for processing the signal and for converting the signal into the data on the thermal conductivity and thermal diffusivity of the solid body is not sufficiently adequate to the physical conditions of the measurements because it does not take into account the heat loss from the heater into the heat insulator and a considerable effect of the contact thermal resistance between the heater and the solid body. Lastly, another serious disadvantage of this method, when used for measuring the thermal conductivity and thermal diffusivity of heterogeneous bodies, consists in the fact that the point temperature sensor is located in one small area (in one point, practically) and responds to the temperature of this small area only. This gives a considerable distortion of the measurement data for the rock which is essentially heterogeneous due to its granularity, fracturing and local variations in the porosity, and makes the measurement data unrepresentative for the total heating area.
There is a known device for measuring the thermal conductivity and thermal diffusivity of solid bodies. It contains a flat sonde 30×90×10 mm in size, which has an internal heat source in the form of thin wires 80, 50 and 30 μm thick and 50 mm long, and three temperature sensors located at a certain distance from the source and used for measuring the temperature gradient between the source center and the distant points of the sonde (Kiyohashi H., Okumura K., Sakaguchi K. and Matsuki K. Development of direct measurement method for thermophysical properties of reservoir rocks in situ by well logging, Proceedings World Geothermal Congress 2000, May 28-Jun. 10, 2000). The sonde is fixed in physical contact with the medium under study. After thermal equilibrium has been reached between the sonde and the medium under study, it is necessary to turn on the heat source and to measure continuously the temperature gradient while introducing corrections for the temperature gradient value in equilibrium. Then, it is necessary to derive the relationship between the temperature gradient measurement data and the observation time and to determine the thermal conductivity and thermal diffusivity of the medium by using the design relationships.
The disadvantages of this device include a low accuracy of measurements in case that the device is used for measuring the thermal conductivity and thermal diffusivity on cylindrical, conical, spherical, elliptical, rough and irregular surfaces, as well as in wells filled with fluid, and the impossibility to achieve a satisfactory thermal contact between the sonde and the medium's wall due to the flat shape of the sonde. Another serious disadvantage of this device includes the distorting effect of the thermal convection of the well fluid, which is possible when the heat from the heater propagates into the surrounding fluid too, thus initiating the convective motion of the fluid and distorting the measurement data. Another disadvantage of this device includes the inconsistency between the theoretical model of the measurement method, developed for using the sonde on flat surfaces of solid bodies, and the real conditions of the measurements taken on solid bodies with non-flat and/or rough or irregular walls. As a result, it is impossible to take into account the effect of the hole wall surface curvature on the thermal conductivity and thermal diffusivity measurement data.
The closest identified analogue of the suggested device is the device used for determining the thermal properties of rock by the flat sonde method, which is based on the regularities of steady-state heat-transfer in a semi-restricted medium on the surface of which a flat heat source is located. The device is described in the article “Flat Sonde Method for Determination of Thermal Properties of Rock in Wells and Mines” by P. I. Filippov, in the book “Methods for Determination of Thermal Properties of Rock”, Moscow, Nauka Publishing House, 1970, pages 107-111. The device includes a flat heater, a point temperature sensor, an elastic heat insulator serving as a heater holder, the sonde body to which the elastic heat insulator is attached, and a hold-down unit to press the sonde body to the surface of the solid bodies. The device heats the solid body surface with a flat heater and measures the flat heater temperature during the heater operation. Based on the flat heater temperature data, the thermal conductivity and thermal diffusivity of the solid body is then determined by using the design relationship.
This device has serious disadvantages which reduce considerably the accuracy of the measurements of the solid body's thermal conductivity and thermal diffusivity and narrow considerably its area of application. Such serious disadvantages include an unacceptably low accuracy of the measurements of the solid body's thermal conductivity and thermal diffusivity, taken on cylindrical, conical, spherical, elliptical, rough and irregular surfaces. The same disadvantage applies to the measurements taken in wells, because this device cannot limit the distorting effect of the thermal convection of the well fluid, which occurs when the flat heater is in operation and when the heat is transferred from the flat heater not only to the solid body, but also to the fluid through the heat insulator, the sonde body and the hold-down unit used for holding down the sonde body. Besides, this device is unable to provide the required accuracy level because it does not take into account the effect of the contact thermal resistance on the measurement data. Another considerable disadvantage of the device consists in the fact that it is impossible to take into account the effect of the shape and irregularities of the solid body surface on the results of the measurements of the solid body's thermal conductivity and thermal diffusivity. The disadvantage of this device, when used for measuring the thermal conductivity and thermal diffusivity of heterogeneous bodies, consists in the fact that the point temperature sensor is located in one small area (in one point, practically) and responds to the temperature of this small area only. This gives a considerable distortion of the measurement data for the rock which is essentially heterogeneous due to its granularity, fracturing and local variations in the porosity, and makes the measurement data unrepresentative for the rock volume corresponding to the heating area.